1. Field of the Invention
The invention relates to a metering device for lubricant having a lubricant reservoir, a piston, which is arranged on a threaded spindle, within the lubricant reservoir and a drive head, which has a drive shaft connected to the threaded spindle and an electromechanical drive for actuating the drive shaft.
2. The Prior Art
In an embodiment known from EP-A 0 845 631, the electromechanical drive has a threaded spindle which is driven by a geared motor. The lubricant reservoir is provided with an outlet opening for lubricant which is ejected by a movement of the piston. The build-up of pressure which can be achieved in the lubricant reservoir is limited. If a large flow resistance builds up at the outlet opening or in an adjoining line, a device protecting against overload responds, switching off the electromechanical drive. The supply of the lubricating points with lubricating products is not always ensured. Furthermore, in the known embodiment, the changing of the lubricant reservoir is complicated. Line systems arranged downstream have to be detached from the lubricant reservoir. If the electromechanical drive is supplied externally with power and/or the lubricant dispenser is connected to a central controller, electric plug-in connections have to be pulled off from the housing before the housing containing the electromechanical drive can be unscrewed from the lubricant reservoir.
Furthermore, lubricant dispensers comprising a piston pump arranged in a housing and a lubricant reservoir connected detachably to the housing are known in practice. A duct which is fixed on the housing is connected to the intake side of the piston pump and opens into the lubricant reservoir. The housing, in which the piston pump, a control device and, if appropriate, batteries for supplying the piston pump with power are arranged, has an outlet duct which is connected to the delivery side of the piston pump. The lubricant reservoir contains a spring-loading piston or expansion bellows which puts the lubricant store under pressure and supplies the generally very viscous lubricating product, for example lubricating grease, to the intake side of the piston pump. The constant pressurization of the lubricating-product store gives rise to the risk of the lubricant bleeding out, i.e. the pressurization by the piston causes small quantities of oil to be continuously ejected out of the grease and thereby causes the lubricating grease to solidify. The piston pump furthermore constitutes a relatively complicated and expensive assembly.